71. 简化路径/535. TinyURL 的加密与解密

71. 简化路径

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/*

.
..
... ? 

这题 用 memcpy 出现了 bug 
memcpy (s1,s2, sizeof(s1))
他是 值比较 S1的长度 

strncpy(s1,s2,sizeof(s1))
这个是比较全部 只是对S 有保护

In short:

strcmp compares null-terminated C strings
strncmp compares at most N characters of null-terminated C strings
memcmp compares binary byte buffers of N bytes

所以这题需要用 strncpy
memcmp 把长度固定死了 超了就会heap溢出

/


*/
#include 
#define FILENUM 1000
#define DOT "."
#define DOUDOT ".."
typedef struct {
    char *file[FILENUM];
    int num;
} File;



char * simplifyPath(char * path){
    if (strlen(path) == 0) {
        return NULL;
    }

    int len = strlen(path) + 1;

    File *fileList = (File *)malloc(sizeof(File));
    memset(fileList, 0, sizeof(File));
    fileList->num = -1;

    char *delim = "/";

    char *token = strtok(path, delim);
    while (token != NULL) {
        if (strncmp(token, DOT, sizeof(token)) != 0 && strncmp(token, DOUDOT, sizeof(token)) != 0) {
            fileList->file[++(fileList->num)] = token;
        } else {
            if (strncmp(token, DOUDOT, sizeof(token)) == 0) {
                if (fileList->num != -1) {
                    fileList->num--;    
                } 
            }
        }
        token = strtok(NULL, delim);
    }
    char *res = (char *)malloc(len);
    memset(res, 0, len);
    if (fileList->num == -1) {
        return "/";
    }

    for (int i = 0; i <= fileList->num; i++) {
        sprintf(res + strlen(res), "/%s", fileList->file[i]);
    }


    return res;
    
}

---

535. TinyURL 的加密与解密

/*
维护一个哈希表 C 不行 C 不能有全局变量 !

只能用 异或
*/

// #define PREFIX "http://tinyurl.com/"
// #define HMSIZE 10000
// #define STRLEN 100

// char *hm[HMSIZE];
// int hmIdx = 0;
// /** Encodes a URL to a shortened URL. */
// char* encode(char* longUrl) {
//     hmIdx++;
//     char *res = (char *)malloc(sizeof(char) * STRLEN);
//     memset(res, 0, STRLEN);
//     memcpy(res, PREFIX, strlen(PREFIX) + 1); // include '\0'
//     sprintf(res + strlen(res), "$%x$", hmIdx);
//     hm[hmIdx] = longUrl;
//     return res;
// }

// /** Decodes a shortened URL to its original URL. */
// char* decode(char* shortUrl) {
//     char *delim = "$";
//     char *ptr = strtok(shortUrl, delim);
//     ptr = strtok(NULL, delim);
//     int hmIdx = atoi(ptr);
//     return hm[hmIdx];
// }
#define ENCRYPTION 0xAB

/** Encodes a URL to a shortened URL. */
char* encode(char* longUrl) {

    for (int i = 0; i < strlen(longUrl); i++) {
        longUrl[i] ^= ENCRYPTION;
    }
    // printf("%s\n", longUrl);
    return longUrl;
}

/** Decodes a shortened URL to its original URL. */
char* decode(char* shortUrl) {
    for (int i = 0; i < strlen(shortUrl); i++) {
        shortUrl[i] ^= ENCRYPTION;
    }
    return shortUrl;
    
}

// Your functions will be called as such:
// char* s = encode(s);
// decode(s);